Replacing text with smiley image using Jquery

Please Guys, I am new to Jquery. I have been searching for a suitable help since last week but I can't find any. I want to replace a text with a smiley image using jquery but I have no idea how to run this. For example, I want this text "I am feeling

:happy;

" to be replaced with "I am feeling

<img src='happy_face.gif' />

" and "He is

:sick;

" to be replaced with "He is

<img src='sick.gif' />

".
Here is what I have gotten so far but it still displays the text instead of the image: